Research activities in this laboratory are directed towards an understanding of the biology and evolution of extrachromosomal (plasmid) elements in Streptococcus ssp. During the current year, we have identified several different types of tetracycline resistant plasmids from group B Streptococcus. Several of these reside on small non-conjugative plasmids which are capable of transforming S. sanguis Challis. For this reason, they are potentially useful as cloning vehicles in this system. We have cloned two tetracycline determinants in the E. coli system using ColEl-amp as the cloning vehicle. These chimeras have been used to generate a large series of deletions which have given a precise definition of the tetracycline resistance region. In addition, we have used the chimeras to make probes for southern hybridization experiments. These experiments have also led to a better understanding of the tetracycline resistance determinants.